Catalytic combustion systems are well known in gas turbine applications to reduce the creation of pollutants, such as NOx, in the combustion process. One catalytic combustion technique known as the rich catalytic, lean burn (RCL) combustion process includes mixing fuel with a first portion of compressed air to form a rich fuel mixture. The rich fuel mixture is passed over a catalytic surface and partially oxidized, or combusted, by catalytic action. Activation of the catalytic surface is achieved when the temperature of the rich fuel mixture is elevated to a temperature at which the catalytic surface becomes active. Typically, compression raises the temperature of the air mixed with the fuel to form a rich fuel mixture having a temperature sufficiently high to activate the catalytic surface. After passing over the catalytic surface, the resulting partially oxidized rich fuel mixture is then mixed with a second portion of compressed air in a downstream combustion zone to produce a heated lean combustion mixture for completing the combustion process. Catalytic combustion reactions may produce less NOx and other pollutants, such as carbon monoxide and hydrocarbons, than pollutants produced by homogenous combustion.
U.S. Pat. No. 6,174,159 describes a catalytic oxidation method and apparatus for a gas turbine utilizing a backside cooled design. Multiple cooling conduits, such as tubes, are coated on the outside diameter with a catalytic material and are supported in a catalytic reactor. A portion of a fuel/oxidant mixture is passed over the catalyst coated cooling conduits and is oxidized, while simultaneously, a portion of the fuel/oxidant enters the multiple cooling conduits and cools the catalyst. The exothermally catalyzed fluid then exits the catalytic oxidation zone and is mixed with the cooling fluid in a downstream post catalytic oxidation zone defined by a combustor liner, creating a heated, combustible mixture.
Typically, gas turbines using catalytic combustion techniques are designed to operate using a fuel having a certain heating value within a predetermined range. The heating value is the amount of energy released when the fuel is burned. However, it may be desired to operate the gas turbine using fuels having heating values outside the predetermined range. If the heating value of the fuel is lower than the predetermined range, the flow rate of the fuel must be increased to obtain the same temperature in the combustion zone.